1. Technical Field
The present invention relates to a plating apparatus for plating a surface (a surface to be plated) of a substrate or the like, and more particularly to a plating apparatus for use in forming a metal film and interconnects on a substrate for LSI circuits or the like according to plating technology, forming a plated film in fine interconnect grooves (trenches), via holes, or resist openings that are defined in a surface of a semiconductor wafer or the like, and forming bumps (protruding electrodes) to be electrically connected to electrodes of a package or the like, on a surface of a semiconductor wafer.
2. Background Art
In recent years, a method of forming interconnects or bumps in semiconductor circuits by forming metallic films on silicon wafers or other substrates according to plating technology has been employed.
In TAB (Tape Automated Bonding) or FC (Flip Chip), for example, it has widely been practiced to form protruding connecting electrodes (bumps) of gold, copper, solder, lead-free solder, or nickel, or a multi-layer laminate of these metals at predetermined portions (electrodes) on a surface of a semiconductor chip having interconnects formed therein, and to electrically connect the interconnects via the bumps with electrodes of a package or TAB electrodes. Methods of forming bumps include various methods, such as electroplating, vapor deposition, printing, and ball bumping. With a recent increase in the number of I/O in a semiconductor chip and a trend toward finer pitches, electroplating has more frequently been employed because it can cope with fine processing and has relatively stable performance.
In particular, metallic films produced by electroplating are advantageous in that they are highly pure, can be grown at high speeds, and have their thicknesses easily controlled. Electroless plating, on the other hand, is advantageous in that the number of steps required to form interconnects or bumps may be small as a seed layer for passing a current on a workpiece to be plated such as a substrate or the like is not required. Since a film formed on a semiconductor substrate is strictly required to be of uniform thickness, many attempts have been made to meet such a requirement in the above plating processes.
FIG. 27 shows an example of a conventional electroless plating apparatus which employs a so-called face-down method. The electroless plating apparatus has an upwardly opened plating tank 12 for holding a plating solution (electroless plating solution) 10 therein, and a vertically movable substrate holder 14 for detachably holding a substrate W as a workpiece to be plated in a state such that a front face (surface to be plated) of the substrate W faces downward (face-down). An overflow tank 16 is provided around an upper portion of the plating tank 12, and a plating solution discharge line 18 is connected to the overflow tank 16. Further, a plating solution supply nozzle 22 is provided at the bottom of the plating tank 12 and connected to the plating solution supply line 20.
In operation, a substrate W held horizontally by the substrate holder 14 is located at a position such as to close an opening at an upper end of the plating tank 12. In this state, the plating solution 10 is supplied from the plating solution supply nozzle 22 into the plating solution tank 12 and allowed to overflow the upper portion of the plating tank 12, thereby flowing the plating solution 10 along a surface of the substrate W held by the substrate holder 14, and returning to a circulation tank (not shown) through the plating solution discharge line 18. Thus, by bringing the plating solution into contact with a pretreated surface of the substrate W, metal is deposited on the surface of the substrate W so as to form a metal film.
According to the plating apparatus, uniformity of the thickness of the metal film formed on the surface of the substrate W can be adjusted to a certain extent by adjusting the supply rate of the plating solution 10 supplied from the plating solution supply nozzle 22, and rotating the substrate holder 14, and the like.
FIG. 28 shows an example of a conventional electroplating apparatus which employs a so-called dipping method. The electroplating apparatus has a plating tank 12a for holding a plating solution (electroplating solution) therein, and a vertically movable substrate holder 14a for detachably holding a substrate W in a state such that a front face (surface to be plated) is exposed while a peripheral portion of the substrate W is water-tightly sealed. An anode 24 is held by an anode holder 26 and disposed vertically within the plating tank 12a. Further, a regulation plate 28 made of a dielectric material having a central hole 28a is disposed in the plating tank 12a so as to be positioned between the anode 24 and the substrate W when the substrate W held by the substrate holder 14a is disposed at a position facing the anode 24.
In operation, the anode 24, the substrate W, and the regulation plate 28 are immersed in the plating solution in the plating tank 12a. Simultaneously, the anode 24 is connected via a conductor 30a to an anode of a plating power supply 32, and the substrate W is connected via a conductor 30b to a cathode of the plating power supply 32. Thus, due to a potential difference between the substrate W and the anode 24, metal ions in the plating solution receive electrons from the surface of the substrate W, so that metal is deposited on the surface of the substrate W so as to form a metal film.
According to the plating apparatus, the variation of the thickness of the metal film formed on the surface of the substrate W can be adjusted to a certain extent by disposing the regulation plate 28 having the central hole 28a between the anode 24 and the substrate W disposed at a position facing the anode 24, and adjusting a potential distribution on the plating tank 12a with the regulation plate 28.
FIG. 29 shows another example of a conventional electroplating apparatus which employs a so-called dipping method. The electroplating apparatus differs from the electroplating apparatus shown in FIG. 28 in that a ring-shaped dummy cathode (dummy electrode) 34 is provided instead of a regulation plate, that a substrate W is held by a substrate holder 14a in a state such that the dummy cathode 34 is disposed around the substrate W, and that the dummy cathode 34 is connected via a conductor 30c to a cathode of a plating power supply 32 during plating.
According to the plating apparatus, uniformity of thickness of a plated film formed on the surface of the substrate W can be improved by adjusting an electric potential of the dummy cathode 34.
FIG. 30 shows still another conventional electroplating apparatus which employs a so-called dipping method. The electroplating apparatus differs from the electroplating apparatus shown in FIG. 28 in that there is no regulation plate, a paddle shaft (stirring mechanism) 36 is positioned above a plating tank 12a and disposed parallel to and between a substrate holder 14a and an anode 24, and a plurality of paddles (stirring rods) 38 are suspended substantially vertically as stirring vanes from a lower surface of the paddle shaft 36, the arrangement being such that, during a plating process, the paddle shaft 36 reciprocally moves the paddles 38 parallel to a substrate W, thereby stirring a plating solution in the plating tank 12a. 
According to the plating apparatus, the paddle shaft 36 reciprocally moves the paddles 38 parallel to the substrate W to uniformize flows of the plating solution (i.e., to eliminate the directivity of flows of the plating solution) along the surface of the substrate W over the entire surface of the substrate W for thereby forming a plated film of more uniform thickness over the entire surface of the substrate W.
For forming a metal film (plated film) as interconnects or bumps on a surface of a semiconductor substrate (wafer), for example, the surface configuration and film thickness of the metal film formed over the entire surface of the substrate are required to be uniform. While highly dense packaging technologies such as SOC, WL-CSP, etc. available in recent years require more highly accurate uniformity, it would be highly difficult for the conventional plating apparatus to produce a metal film that meets the requirements for such highly accurate uniformity.
Specifically, each of the conventional plating apparatuses has its own structural features that result in the film thickness variation characteristics of a plated film formed thereby, and to produce a plated film having better film thickness uniformity, improvement of the plating apparatus is required. For producing a plated film of uniform film thickness, it is effective to uniformize flows of the plating solution near a surface to be plated of a substrate or the like. There is a demand for a process of making a uniform flow of plating solution and bringing the plating solution into contact with a surface to be plated of a substrate or the like. Plating apparatus themselves are also required to have a simple structure and mechanism designed for easy maintenance. For example, the plating apparatus shown in FIG. 29 needs to be operated so as to adjust a dummy electrode and remove plated metal that has been deposited on the dummy electrode. It has been desired to handle the plating apparatus better and manage the plating apparatus simply and without the problems of operation and management complexities. For shortening the plating time, it is very desirable to increase the plating speed. Increasing the plating speed requires supplying metal ions in the plating solution efficiently to a surface to be plated of a substrate or the like.
In electroplating, one approach to increase the plating speed would be to increase the current density. However, simply increasing the current density would cause burnt deposits, plating defects, passivation of the anode surface, etc., possibly resulting in plating failures.